1. Field of Invention
This invention relates to a method and apparatus for producing three-dimensional objects layer by layer using a powdery material which can be solidified by irradiating it with a high-energy beam.
2. Description of Related Art
Equipment for producing a three-dimensional object layer by layer using a powdery material which can be solidified by irradiating it with electromagnetic radiation or an electron beam are known from e.g. U.S. Pat. Nos. 4,863,538, 5,647,931 and WO 2004/056511. Such equipment include for instance a supply of powder, means for applying a layer of powder onto a working area of a work table, and means for directing the beam over the working area. The powder sinters or melts and solidifies as the beam moves or sweeps over a working area.
For product quality reasons it is important that the applied layer of powder is evenly distributed over the working area and that the layer thickness is well-defined and corresponds to a predetermined value. Further, it is advantageous that the layer is quickly applied in order to keep the production rate as high as possible.
Traditionally, powder application means includes a feeding member and a distribution member where the former transfers a certain quantity of powder from the supply of powder to the distribution member, which in turn distributes the powder over the working area. WO 2006/121374 discloses another variant wherein a distribution rake is arranged to be moveable towards and a certain distance into the powder supply such as to work both as feeding member and distribution member.
For quality assurance reasons, and for making it possible to e.g. re-apply a layer of powder if the powder distribution is not correct, it would be desirable to determine the thickness and homogeneity of a layer of powder that has been applied onto the working area. However, how to do this in an easy and efficient way is not evident, irrespective of what type of powder application means that are used. Therefore, focus has generally been set on improving the reliability of the powder application systems.
An example of a system for monitoring the surface height/thickness of a layer in a selective deposition modelling (SDM) apparatus is disclosed in U.S. 2002/0104973. The system makes use of a light source, such as a laser, that directs a beam of light downwards towards the layer of non-solidified build material. A light detector, arranged at an angle in relation to the light source, detects scattered light from the surfaces of the non-solidified layer and the solidified layer below. The thickness of the non-solidified layer is then calculated by means of triangulation. The application described makes use of a liquid build material. Although the system disclosed may work well in certain situations it will not work properly when non-transparent build materials are used, such as metal powder. Further, the system requires additional equipment that is difficult and expensive to install in some types of apparatuses.
Thus, there is still a need for a system/method for checking the thickness and distribution of a layer of powder that has been applied onto the working area, in particular in cases where metal powder is used.